Lubricant composition

ABSTRACT

Provided is a lubricant composition derived from renewable materials and that is useable in cold weather conditions and exhibits oxidative stability. The lubricant composition comprises a polymer of Formula (I), wherein R and p are as described in this specification.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from provisional application Ser. No. 61/468,625, filed Mar. 29, 2011, which is incorporated herein by reference in its entirety.

BACKGROUND

The invention relates generally to lubricant compositions and to methods of their preparation and use. More particularly, the invention relates to lubricant compositions that may be prepared from renewable sources and that exhibit a combination of favorable viscosity, stability, and pour point characteristics.

“Bio-lubricants,” or lubricants based upon renewable resources such as seed oils and vegetable oils rather than from petroleum or natural gas, represent a small, but growing segment of total global lubricants demand. Natural esters (for example, canola oil) and synthetic esters can be used to formulate bio-lubricants that conform to the requirements of the European Eco-label (European Commission 2005/360/EC). These formulations must contain certain minimum levels of renewable carbon atoms in the formulation in order to meet the EC requirements. As an example, hydraulic fluids require a minimum level of renewable carbons of at least 50 percent.

To be useful in a broad array of applications, biolubricants need to meet a number of technical performance criteria. In particular, materials that show acceptable viscosity at low and high temperatures, and have high viscosity index values (preferably greater than 140) as well as good cold weather properties, and contain a high percentage of renewable carbons, have generally been elusive. As a consequence, many biolubricants are not optimal for use in applications where these performance criteria are needed including, for instance, applications where very low temperatures may be experienced, such as with outdoor mobile equipment.

In addition to viscosity and cold weather performance criteria, another desirable feature is oxidative stability. That is, the lubricant composition, when it contains an antioxidant, exhibits a viscosity that remains substantially stable even when the composition is subjected to prolonged heating.

STATEMENT OF INVENTION

We have now discovered new lubricant compositions that may at least partially be based on renewable materials and that also exhibit favorable low and high temperature viscosity, exhibit high viscosity indices, and exhibit very low pour points. Advantageously, therefore, the lubricants are well suited for use under a variety of temperature conditions, including temperatures at −40° C. and lower. In addition, the compositions exhibit excellent oxidative stability, experiencing little viscosity fluctuation even after prolonged heating.

In one aspect, there is provided a lubricant composition comprising a polymer represented by the formula I:

wherein p is an integer or fraction from 1 to 5, R at each occurrence is independently a group of the formula:

n is an integer from 6 to 13, one of R¹ and R² is H and one is linear or branched C₁-C₇ alkyl, and m is an integer or fraction from 2 to 5.

In another aspect, there is provided a method for lubricating an apparatus, comprising providing a lubricant composition as described herein.

In another aspect, there is provided a method for making the polymer of formula I, the method comprising: (a) reacting a polyol and an alkylene oxide compound under alkoxylation conditions to form an alkoxylate; and (b) esterifying the alkoxylate of step (a) with a fatty acid or its alkyl ester under esterification conditions.

DETAILED DESCRIPTION

Unless otherwise indicated, numeric ranges, for instance as in “from 2 to 10,” are inclusive of the numbers defining the range (e.g., 2 and 10).

Unless otherwise indicated, ratios, percentages, parts, and the like are by weight.

In some embodiments, p in the polymer of formula I is a fraction between 1 and 5, alternatively it is a fraction between 2 and 5, or alternatively it is a fraction between 2 and 3. In some embodiments, p is 2. In some embodiments, p is 3.

In some embodiments, R¹ in the polymer of formula I is H and R² is methyl.

In some embodiments, m is an integer or fraction from 2 to 3. In some embodiments, m is a fraction between 2 and 3.

In some embodiments, n is an integer from 7 to 9. In some embodiments, n is 8.

Polymers of formula I may be prepared by a process comprising an alkoxylation step and an esterification step. In the alkoxylation step, a polyol may be mixed with an alkoxylation catalyst, such as aqueous potassium hydroxide, flushed with an inert gas, and heated under reduced pressure in order to remove water from the mixture. When the desired water content is reached, e.g., 1500 ppm or less, the pressure may be increased and an alkylene oxide introduced to the reaction mixture. Typically, the addition and reaction may be conducted at elevated temperature, such as 120 to 140° C. Following a digestion time, e.g., 4-6 hours, the alkoxylated product may be isolated.

The polyol of the alkoxylation step may be a polyglycerine compound or mixture of compounds represented by the formula A:

wherein p in each compound is an integer from 1 to 5, preferably 2 to 3. Various polyglycerines of the foregoing formula are available from renewable sources. For instance, polyglycerines in which p is 2 (diglycerine) and p is 3 (triglycerine) and their mixtures are available from bio-glycerine.

The alkylene oxide is preferably propylene oxide or butylene oxide, more preferably it is propylene oxide.

In the esterification step, the alkoxylate, a catalyst such as titanium (IV) isopropoxide, and a fatty acid or a fatty acid derivative, such as or its alkyl ester (e.g., its methyl ester), anhydride, or chloride are mixed and heated, for example to 150 to 170° C., under an inert gas, to effect the esterification reaction. Vacuum may be applied during the reaction in order to remove formed water or alcohol byproduct. The temperature may be further facilitated by increasing the temperature and/or reducing the pressure. Following sufficient time for the reaction to occur, e.g., 1-3 hours, the product mixture may be cooled and the esterified product isolated.

Suitable fatty acids for the esterification step include, for example, octanoic acid, nonanoic acid, decanoic acid, undecanoic acid, dodecanoic acid, tridecanoic acid, tetradecanoic acid, or pentadecanoic acid. In some embodiments, the methyl ester of the foregoing acids is preferred. In some embodiments, the fatty acid is decanoic acid or its methyl ester, methyl decanoate. The foregoing acids and esters may be obtained from a variety of renewable sources, such as natural esters (e.g. palm oil, castor oil, rapeseed oil and soybean oil).

As noted above, the polymers of formula I may be prepared from renewable polyols and fatty acids (or derivatives) and may be produced to contain at least 50 percent renewable carbons, alternatively at least 60 percent renewable carbons, or alternatively at least 70 percent renewable carbons. As a result, in some embodiments, lubricant composition which comprise the polymers may conform to the requirements of the European Eco-label (European Commission 2005/360/EC).

Polymers of formula I exhibit highly favorable pour points, making them useful in very cold weather environments. In some embodiments, the polymers exhibit a pour point of −40° C. or less, alternatively −45° C. or less, or alternatively −50° C. or less (when measured in the absence of pour point depressants such as polyakylene-methacrylates or styrene/maleic anhydride interpolymers). Pour point may be measured in accord with American Society for Testing and Materials (ASTM) D97-87.

Polymers of formula I also exhibit favorable viscosity profiles over a wide temperature range. In some embodiments, the polymers exhibit a kinematic viscosity at 40° C. (V40) of at least 30 cSt (centistokes) alternatively at least 40 cSt, alternatively at least 50 cSt, alternatively at least 55 cSt, or alternatively at least 60 cSt. In some embodiments, the polymers of formula I exhibit a kinematic viscosity at 100° C. (V100) of at least 7 cSt, alternatively at least 8 cSt, alternatively at least 9 cSt, alternatively at least 10 cSt, or alternatively at least 12 cSt. In some embodiments, the polymers of formula I exhibit a V40 of at least 50 cSt and a V100 of at least 9 cSt. Viscosity (kinematic) may be measured using a Stabinger viscometer in accord with ASTM D7042.

Additionally compositions of the invention demonstrate favorable oxidative stability profiles. That is, when the composition includes a polymer of formula I and an anti-oxidant, it exhibits a narrow kinematic viscosity change when heated at elevated temperature for extended periods of time. Oxidative stability may be measured using ASTM D2893B. According to the method, the formula I polymer plus an antioxidant are heated to 121° C. in dry air for 13 days. The kinematic viscosity of the fluid at 100° C. (KV100) before and after the test is recorded according to ASTM D7042 and the percentage viscosity change is recorded.

In some embodiments of the invention, the compositions exhibit a kinematic viscosity change at 100° C., using the foregoing test, of 8 percent or less, alternatively 6 percent or less, or alternatively 4.3 percent or less.

Lubricant compositions of the invention have utility as, for example, hydraulic fluids. Hydraulic fluids are used in a variety of apparatus common to industrial segments including mining, steel, die-casting, and food processing, as well as forestry and marine equipment, and outdoor mobile equipment. Furthermore, such lubricant compositions also have potential utility in the automotive segment as, for example, engine oils, transmission fluids, compressor fluids, and gear oils or as components of such oils or fluids. Skilled artisans who work with lubricant compositions readily understand other suitable end use applications for the lubricant compositions of the present invention.

Some embodiments of the invention will now be described in detail in the following Examples.

EXAMPLES

Polymers for evaluation in the examples may be prepared as follows.

Alkoxylation Procedure:

Alkoxylations are carried out on a 10 liter stainless steal reactor which is temperature controlled via an external thermostatic control unit containing silicone oil. The oxide dosing system is controlled by weight and limited by a maximum pressure in the reactor of 4.5 bar.

Polyol and catalyst (45 wt % KOH in water) are charged into the reactor at 50° C. In order to limit discoloration due to oxidation reactions the reactor is flushed five times with nitrogen. The stirrer is started and the speed is set to 500 rpm. Next the reactor content is brought to 100° C. and vacuum is applied (30 mbar) in order to remove the water from the initiator/catalyst mixture. The oxide feeding bomb is filled with propylene oxide (PO). After typically 1 hour flashing, samples are taken from the mixture in the reactor and water content is determined by titration. When the water content reaches the desired value (typically 1500 ppm), water flashing is stopped and the reactor pressure is brought to 1.2 bars (with nitrogen). The temperature of the mixture in the reactor is increased to 130° C. After reaching the reaction temperature, the oxide feed is started. The maximum gauge pressure in the reactor is 4.5 bars. After a digest time of 5 hours (or more) the reactor content is cooled to 60° C. Magnesium silicate (MagSil) is added (to adsorb the KOH catalyst) and stirred for approx 30 min. Typically 8 grams of MagSil is charged into the reactor for every gram of KOH catalyst. Next the mixture is taken out of the reactor and filtered using a buchner funnel and paper filter (type 604 from Scheicher & Schuell) until the product is clear.

Esterification Procedure:

The setup includes a glass reactor with a temperature control unit, a stirrer, nitrogen sparger/blanket and sampling port Attached to the reactor is a dean stark that allows separating the entrainer phase from the by-product. Between the reactor and the Dean-Stark, a distillation column (Vigreux column) can be placed to improve distillation efficiency. A second collecting cold trap is placed after the condenser to increase volatiles recovery when being removed. A vacuum pump is connected to the system and is used to aid volatiles removal process from the reaction mixture.

All raw materials and the catalyst titanium (IV) iso-propoxide are placed in the reactor and the mixture is heated to 160° C. on a nitrogen atmosphere. The vacuum pump is set to 100 mBar an then the system switched from nitrogen to vacuum. Methanol formed during the reaction is collected in the Dean-Stark receiver. Once the theoretical amount of methanol is collected or no more methanol is condensing in the receiver, the vacuum is set to 15 mBars end excess ester is removed from the mixture. To facilitate removal the temperature is set to 190° C. and the mixture is left under reduced pressure for 1 hour. After completion of this step the mixture is cooled to approximately 70° C. and then filtered over magnesium silicate.

Viscosity and Pour Point Performance

Table 1 lists polymers, starting materials, and various of their properties, which may be prepared substantially as described above. Products numbers 1-4 are representative of the invention, whereas product numbers C1-C4 are comparative examples and not of the invention.

TABLE 1 Summary of Properties Product No. 1 2 3 4 C1 C2 C3 C4 Starter PG2 PG2 PG3 PG2 TMP IP200 PG2 PG2 Mol's PO 12 9 11 9 6 — 9 9 Fatty acid C10 sat C10 sat C10 sat C10 sat C10 sat C10 sat C16/C18 Oleic (or its sat methyl ester) V40 (cSt) 68.5 56.1 78.3 62.1 42.9 13.5 71.7 69.0 V100 (cSt) 11.8 9.96 12.9 10.5 8.01 3.57 12.1 13.4 Viscosity 171 167 167 161 162 156 168 202 Index Pour point −52 −56 −53 −53 −56 −50 −28 −33 (° C.) Renewable 56 63 64 63 56 62 73 74 Carbon content (%) PG2 = diglycerine (formula I cmpd where p = 2); PG = triglycerine (formula I cmpd where p = 3), TMP = trimethylopropane; IP = polypropylene glycol (average mol weight 200 g/mole); PO = propylene oxide; C10 sat = decanoic acid or its methyl ester; C16 sat = hexadecanoic acid or its methyl ester; C18 sat = octadecanoic acid or its methyl ester; Oleic = oleic acid or its methyl ester

As can be seen from the data in the Table, products according to the invention (numbers 1-4) provide a combination of excellent pour point characteristics and high viscosity indices. In contrast, Formulations C3 and C4 show high pour points and formulation C2 shows a low viscosity at 40° C. which is not practical for use in many lubricant applications.

Oxidation Test Performance

The oxidation stabilities of some of the compositions described above are examined using ASTM D2893B. To each polymer is added 1% IRGANOX® L57 and 0.5% IRGANOX® L101 as anti-oxidants (both available from BASF). A summary of the oxidation method is as follows.

The test lubricant (300 ml) in a borosilicate glass tube is heated to 121° C. in dry air for 13 days. The kinematic viscosity of the fluid at 100° C. (KV100) before and after the test is recorded according to ASTM D7042 and the percentage viscosity change is recorded. Desirable fluids are those which show a viscosity change of less than 6%.

Results for various compositions are shown in Table 2. Two reference fluids are also evaluated in the test (in addition to the comparative compositions).

TABLE 2 Oxidation performance using ASTM D2893B % Viscosity change Product No. after 13 days 2 3.1 3 4.3 4 3.5 C1 8.9 C3 4.5 C4 168 Canola oil - reference 516 Trimethylolpropane trioleate (SYNATIVE 305 TMP-05 from Cognis)- reference

Table 2 shows that compositions of the invention (numbers 2-4) exhibit excellent oxidation stability and a viscosity change of <6%. In contrast C1 and C4 and the two reference fluids show higher values. 

What is claimed is:
 1. A lubricant composition comprising a polymer represented by the formula I:

wherein p is 2 or 3 or fraction between 2 and 3, R at each occurrence is independently a group of the formula:

n is an integer from 6 to 13, one of R¹ and R² is H and one is linear or branched C₁-C₇ alkyl, and m is an integer or fraction from 2 to
 5. 2. (canceled)
 3. The lubricant composition of claim 1 wherein R¹ is H and R² is methyl.
 4. The lubricant composition of claim 1 wherein m is an integer or fraction from 2 to
 3. 5. The lubricant composition of claim 1 wherein n is an integer from 7 to
 9. 6. The lubricant composition of claim 1 wherein the polymer exhibits a viscosity at 40 degrees Celsius (V40) of at least 30 centistokes and a viscosity at 100 degrees Celsius (V100) of at least 7 centistokes.
 7. The lubricant composition of claim 1 wherein the polymer exhibits a viscosity at 40 degrees Celsius (V40) of at least 50 centistokes and a viscosity at 100 degrees Celsius (V100) of at least 9 centistokes.
 8. The lubricant composition of claim 1 wherein the polymer exhibits a pour point of −40 degrees Celsius or lower without a pour point depressant.
 9. A method of lubricating an apparatus, comprising providing a lubricant composition according to claim
 1. 10. A method for making the polymer of claim 1, the method comprising: (a) reacting a polyol and an alkylene oxide compound under alkoxylation conditions to form an alkoxylate; (b) esterifying the alkoxylate of step (a) with a fatty acid or its alkyl ester under esterification conditions to form the polymer of claim
 1. 